Everyone thanks so much for your reply!
It is clear to me now that the SSL certificate sent by Bitpay is not accepted by Electrum and it's not possible to manually edit this. It is something Bitpay has to fix.
In the mean time one can use a decoder (like
https://alexk111.github.io/DeBitpay/ ) to extract the payment details. Alternatively you can tell Bitpay you're using Samourai Wallet (which does not support payment protocol), Bitpay should then show the details to manually make the payment.
It's the
BIP-70 protocol (the one BitPay invoices use).
Bitcoin Core removed support for BIP-70, and I think Electrum did too.
In other words, not all wallets support BIP-70; most use BIP-21 (Bitcoin URI).
Is bitpay still insists on BIP-70 today? This only makes things more complicated and negatively impacts the user experience.
I recommend using a different wallet or a BIP-70 decoder to extract payment information, as suggested by DaveF.
This is bizarre. Tell me the name of the store using bitpay so I can test it.
Oohhhh, if I'm not mistaken, bitpay displays wallet options when paying invoices and payment instructions. Can you confirm this? I recall that being the case.