Ghost and Stripe lost connection - apiKey should be a string

Hi guys,

I have problem with my website
Everything worked correctly but suddenly visitors started complaining they could not buy subscription. This error occurred while trying to submit order:

Missing value for Stripe(): apiKey should be a string.

It is possible this happened after upgrading to * Version: [5.26.4]
We are trying to find out.

Our Ghost is self hosted - Digitalocean

Can someone help us with this problem?