Unable to receive transaction from Shopify to our Payment Gateway

Hello everyone/Shopify Support,

We are currently facing an issue (since 3rd July, 4PM GMT) where we are no longer receiving any transactions from Shopify. Everything seems fine on our end. We believe the problem might be related to an expired certificate or an SSL certificate issue.

Has anyone encountered this before or could help us resolve it?

Thank you in advance for your support!