Web Viewer and Paypal Sandbox - can't login to my facillitator account on paypal sandbox

I am using a web pages 'mobile_app.php' to process user input from my app.
That includes when the user clicks on a Paypal button.

mobile_app.php
Ommitting a lot of irrelevant code...
All I want to see is what the paypal web site returns

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	if (isset($_GET["button"]) || isset($_GET["paypal"]))
	{
		$_POST = $_GET;
	}				
	.
	.
	.
	.
	.
	.
	else if (isset($_POST["paypal"]))
	{
		echo "OK" . $_POST["paypal"];
	}
	else if (!empty($_POST))
	{
		$strPurpose = "";
		$strMemeberID = "";
		DoGetFileUploadPurpose($strPurpose, $strMemberID);

		if ($strPurpose == $g_strProfile)
		{
			$strProfileImageFilename = DoGetProfileImageFilename($strMemberID);
			$data = file_get_contents('php://input');
			file_put_contents("images/" . $strProfileImageFilename, $data);
			echo "OK";
		}
	}
	else
	{
		//print_r($_POST);
	}

?>
		
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">

	<head>
		<meta content="text/html; charset=utf-8" http-equiv="Content-Type" />
		<title>PAYPAL</title>
	</head>
	
	<body>

		<table class="paypal_table">
			<tr>
				<td class="paypal_cell paypal_first_cell" width="120">1 month</td>
				<td class="paypal_cell paypal_first_cell" width="60">$<?php printf("%0.2f", $g_nCostPerMonth); ?></td>
				<td class="paypal_cell paypal_first_cell">
					<div id="live1" style="display: <?php echo $g_strPaypalLive; ?>;">
						<form action="https://www.paypal.com/cgi-bin/webscr" method="post" target="_top">
							<input type="hidden" name="cmd" value="_s-xclick" />
							<input type="hidden" name="hosted_button_id" value="ML57FQAQM8FBY" />
							<input type="hidden" name="currency_code" value="AUD" />
							<input type="image" src="https://www.paypalobjects.com/en_AU/i/btn/btn_paynowCC_LG.gif" border="0" name="submit" title="PayPal - The safer, easier way to pay online!" alt="Buy Now" />
						</form>
					</div>
					<div id="debug1" style="display: <?php echo $g_strPaypalTest; ?>;">
						<form action="https://www.sandbox.paypal.com/cgi-bin/webscr" method="post" target="_top">
							<input type="hidden" name="cmd" value="_s-xclick" />
							<input type="hidden" name="hosted_button_id" value="YBHPW5W868SCA" />
							<input type="hidden" name="currency_code" value="AUD" />
							<input type="image" src="https://www.paypalobjects.com/en_AU/i/btn/btn_paynowCC_LG.gif" border="0" name="submit" title="PayPal - The safer, easier way to pay online!" alt="Buy Now" />
						</form>
					</div>
				</td>
			</tr>
			<tr><td colspan="3"><br/><br/></td></tr>
			<tr>
				<td class="paypal_cell" width="120">6 months</td>
				<td class="paypal_cell" width="60">$<?php printf("%0.2f", $g_nCostPerMonth * 6); ?></td>
				<td class="paypal_cell">
					<div id="live6" style="display: <?php echo $g_strPaypalLive; ?>;">
						<form action="https://www.paypal.com/cgi-bin/webscr" method="post" target="_top">
							<input type="hidden" name="cmd" value="_s-xclick" />
							<input type="hidden" name="hosted_button_id" value="MSH56S2JA7R9Y" />
							<input type="hidden" name="currency_code" value="AUD" />
							<input type="image" src="https://www.paypalobjects.com/en_AU/i/btn/btn_paynowCC_LG.gif" border="0" name="submit" title="PayPal - The safer, easier way to pay online!" alt="Buy Now" />
						</form>				
					</div>
					<div id="debug6" style="display: <?php echo $g_strPaypalTest; ?>;">
						<form action="https://www.sandbox.paypal.com/cgi-bin/webscr" method="post" target="_top">
							<input type="hidden" name="cmd" value="_s-xclick" />
							<input type="hidden" name="hosted_button_id" value="NYX3H2YG5WXL4" />
							<input type="hidden" name="currency_code" value="AUD" />
							<input type="image" src="https://www.paypalobjects.com/en_AU/i/btn/btn_paynowCC_LG.gif" border="0" name="submit" title="PayPal - The safer, easier way to pay online!" alt="Buy Now" />
						</form>
					</div>
				</td>
			</tr>
			<tr><td colspan="3"><br/><br/></td></tr>
			<tr>
				<td class="paypal_cell" width="120">12 months</td>
				<td class="paypal_cell" width="60">$<?php printf("%0.2f", $g_nCostPerMonth * 12); ?></td>
				<td class="paypal_cell">
					<div id="live12" style="display: <?php echo $g_strPaypalLive; ?>;">

					</div>
					<div id="debug12" style="display: <?php echo $g_strPaypalTest; ?>;">
						<form action="https://www.paypal.com/cgi-bin/webscr" method="post" target="_top">
							<input type="hidden" name="cmd" value="_s-xclick" />
							<input type="hidden" name="hosted_button_id" value="7MXQ5HRMGLC3N" />
							<input type="hidden" name="currency_code" value="AUD" />
							<input type="image" src="https://www.paypalobjects.com/en_AU/i/btn/btn_paynowCC_LG.gif" border="0" name="submit" title="PayPal - The safer, easier way to pay online!" alt="Buy Now" />
						</form>
					</div>
				</td>
			</tr>
			<tr><td colspan="3"><br/><br/></td></tr>
			<tr>
				<td class="paypal_cell" width="120">18 months</td>
				<td class="paypal_cell" width="60">$<?php printf("%0.2f", $g_nCostPerMonth * 18); ?></td>
				<td class="paypal_cell">
					<div id="live18" style="display: <?php echo $g_strPaypalLive; ?>;">
						<form action="https://www.paypal.com/cgi-bin/webscr" method="post" target="_top">
							<input type="hidden" name="cmd" value="_s-xclick" />
							<input type="hidden" name="hosted_button_id" value="B4HP8BQ4VE3QY" />
							<input type="hidden" name="currency_code" value="AUD" />
							<input type="image" src="https://www.paypalobjects.com/en_AU/i/btn/btn_paynowCC_LG.gif" border="0" name="submit" title="PayPal - The safer, easier way to pay online!" alt="Buy Now" />
						</form>
					</div>
					<div id="debug18" style="display: <?php echo $g_strPaypalTest; ?>;">
						<form action="https://www.sandbox.paypal.com/cgi-bin/webscr" method="post" target="_top">
							<input type="hidden" name="cmd" value="_s-xclick" />
							<input type="hidden" name="hosted_button_id" value="6GDHY53HDNLPQ" />
							<input type="hidden" name="currency_code" value="AUD" />
							<input type="image" src="https://www.paypalobjects.com/en_AU/i/btn/btn_paynowCC_LG.gif" border="0" name="submit" title="PayPal - The safer, easier way to pay online!" alt="Buy Now" />
						</form>
					</div>
				</td>
			</tr>
			<tr><td colspan="3"><br/><br/></td></tr>
			<tr>
				<td class="paypal_cell" width="120">24 months</td>
				<td class="paypal_cell" width="60">$<?php printf("%0.2f", $g_nCostPerMonth * 24); ?></td>
				<td class="paypal_cell">
					<div id="live24" style="display: <?php echo $g_strPaypalLive; ?>;">
						<form action="https://www.paypal.com/cgi-bin/webscr" method="post" target="_top">
							<input type="hidden" name="cmd" value="_s-xclick" />
							<input type="hidden" name="hosted_button_id" value="WNJ2DTPLE2V2W" />
							<input type="hidden" name="currency_code" value="AUD" />
							<input type="image" src="https://www.paypalobjects.com/en_AU/i/btn/btn_paynowCC_LG.gif" border="0" name="submit" title="PayPal - The safer, easier way to pay online!" alt="Buy Now" />
						</form>									
					</div>
					<div id="debug24" style="display: <?php echo $g_strPaypalTest; ?>;">
						<form action="https://www.sandbox.paypal.com/cgi-bin/webscr" method="post" target="_top">
							<input type="hidden" name="cmd" value="_s-xclick" />
							<input type="hidden" name="hosted_button_id" value="5MEDPTLFQF3JU" />
							<input type="hidden" name="currency_code" value="AUD" />
							<input type="image" src="https://www.paypalobjects.com/en_AU/i/btn/btn_paynowCC_LG.gif" border="0" name="submit" title="PayPal - The safer, easier way to pay online!" alt="Buy Now" />
						</form>
					</div>
				</td>
			</tr>
		
		</table>						

	</body>
		
</html>

I am returning what the user selected, in terms of membership renewal period (1, 6, 12, 18, 24 months) as GET data to the web viewer in my app.

As stated the web viewer won;t let me login in to my facillitator account on paypal sandbox.
If I view mobile_app.php i Firefox on my laptop, press the paypal button then I can log in to my faciitator account just fine.
The web viewer component in MIT App inventor is blocking it some how. Why?

Do you get an error ?

Show the login attempt, what happens ?