It sounds like you've covered all the basic troubleshooting steps by creating a new secret API key and testing it with Stripe. Since you have experience with other API keys and they are working fine, it's indeed puzzling why this issue is occurring specifically with Machform.
A couple of suggestions to explore further:
Check for Error Logs: Have you checked for any error logs in Machform or your server's error logs? These logs can often provide valuable insights into what might be going wrong.
Cross-Origin Resource Sharing (CORS): Ensure that CORS settings for your API key are correctly configured if required. Sometimes, API requests can fail due to CORS issues.
Network Monitoring: Use browser developer tools or network monitoring tools to inspect the network requests when the payment page doesn't load. This might reveal more details about the problem, such as any failed requests or error messages.
Machform Support: Reach out to Machform's support or community forums. They may have encountered similar issues and can provide specific guidance for integrating Stripe API keys with their platform.
Browser Extensions: Disable any browser extensions that might interfere with the loading of the payment page. Sometimes, ad blockers or privacy extensions can cause issues.
SSL/TLS Certificate: Ensure that your website has a valid SSL/TLS certificate. Stripe often requires secure connections, and issues can occur if your certificate is expired or misconfigured.
Server Configuration: Double-check your server configuration, including PHP settings and server environment variables, to ensure they align with the requirements for Machform and Stripe integration.
Stripe Webhooks: Ensure that you have configured any necessary Stripe webhooks correctly. They are crucial for handling events related to payments on our store and can help with debugging.