@Andrew BAN I'm glad that you were able to resolve your issue and thank you for posting your solution so that others experiencing the same thing can easily reference this! Since the Microsoft Q&A community has a policy that "The question author cannot accept their own answer. They can only accept answers by others ", I'll repost your solution in case you'd like to "Accept " the answer.
Also came across this stackoverflow post - [https://stackoverflow.com/questions/59951424/azure-market-place-sendgrid-username talks about similar issue where first answer in the post (most voted) wanted to update here as it would help other community members facing similar issue.