If your old iOS device cannot run the latest Messenger, open Safari and go to mbasic.facebook.com/messages/ . It’s not perfect, but it works on almost any browser.

: Sideloaded IPAs usually require a developer certificate. If you use a free Apple ID, the app will expire every 7 days and need to be refreshed.

Short installation checklist (for post footer):

If you need to test against Messenger’s APIs, use the official SDK or Graph API, not a reverse-engineered IPA.