Hi David,
There is a known issue that has been happening for the last 1+ week whereby if you try to create a Web App or Azure Function you will receive error similar to Forbidden/BadGateway The subscription <subscriptionId> is not allowed to create or update the serverfarm.
Approximately 50-75 people have reported here on Q & A that they are experiencing the problem.
Until Microsoft fixes the issue, your options are basically a) wait and keep trying periodically in same and/or different regions or b) create a new technical support request and a support engineer will fix it on the backend. Unfortunately option b requires a paid Azure support plan (you can pay only for 1 month and cancel if you want).
If you want to create Technical support request, you need to first upgrade to at least Developer support. Below link will allow you to do that via the Azure portal:
https://portal.azure.com/#view/Microsoft_Azure_Support/HelpAndSupportBlade/~/supportPlans
After you have a paid support plan, below link has instructions for creating new support request:
Create an Azure support request
NOTE: It can be confusing to create support request. If it seems like you are stuck in a "loop" whereby you only get recommended solutions/links, please look for Return to support request in upper left, click it, click Next, etc.
Issue The subscription is not allowed to create or update the serverfarm
Please click Accept Answer and upvote if the above was helpful. If something is unclear please add a comment.
Thanks.
-TP