1. Open Signal and click on your user icon in the upper left.
2. Go to "Settings" --> "Donate to Signal".
3. Click "Donate", select your donation options, and pay with Apple Pay.
Your payment info is not connected to your account.
https://support.signal.org/hc/en-us/articles/360031949872-Do...
Does Apple have any records connecting your recurring Apple Pay payment to your iPhone's phone number?