The Product block's price is fixed per block, not a reader-entered amount, so a true "pay what you want" field isn't something MailInApp renders directly. A few Product blocks side by side, each a different fixed tip tier, gets most of the way there — a real Stripe charge on your own account either way.
Most readers who want to tip don't need infinite flexibility on the amount — a small, medium, and generous option covers the overwhelming majority of what a pay-what-you-want field would have collected anyway.
Fixed tiers instead of a free-entry field
Add two or three Product blocks at different prices — say $3, $10, $25 — each with Digital fulfillment and a short thank-you message as the delivery content. A tip has nothing physical to fulfill, so the "download" is just the note itself, emailed automatically the instant payment confirms.
Cover the truly custom amount too
A Button linking out to an external pay-what-you-want page (Ko-fi, Buy Me a Coffee, your own site) catches anyone who wants to give an amount that doesn't match one of the fixed tiers, without forcing everyone else through an extra hop.
It settles on your own Stripe account
Every tip is a real charge on your own connected Stripe account via Stripe Connect — checkout is commission-based on top of Stripe's own processing fees, and MailInApp never holds the funds.
Fold it into content people already open
A tip jar works better attached to a newsletter, episode drop, or update email than sent as its own dedicated ask — the Rating block alongside it ("how was this issue?") gives supporters something to respond to either way.
Getting started
Add two or three Product blocks at different fixed tip amounts, each with Digital fulfillment and a thank-you note as the delivery content, plus a Button linking to an external pay-what-you-want page for custom amounts. Send it as part of your regular content rather than a standalone message.