PayPal express checkout buttons do not show up on the product page

[SaaSQuadrat]

I am to finish a shop for a client: https://dressupmysalad.com/

What happened / we did:

• The first Testorder we did, was a payment with PayPal, which showed up in Shopify with status unpaid but was not displayed in PayPal yesterday. At this point in time the PP express checkout button showed on the product page
• Hence, we assumed there is an issue and disabled PayPal yesterday for the shop.
• After the transaction now shows in PayPal we activated PayPal payments in the shop again.
• Now the express PP button does not show on the product page

PayPal shows in the checkout page and I logged in with paypal, which worked. Just didn't confirm the order.

Somehow the deactivation and later reactivation of the PayPal payment method seems to have broken the express checkout.

What to do?