With a major port at Chester ( Dewa), a Mersey crossing and significant settlement at Warrington (Wilderspool), and a major centre at Wigan (Coccium), like many before them, the Romans seemingly didn’t see much worth bothering with in Sefton.
There have been some finds of Roman coins at Otterspool ( 1863) and Sefton Park ( 1871), but no indications that there was anything of note happening. Apart from taxes going to a different overlord and different coinage, it is unlikely that life changed a great deal for Merseysiders. Again, without natural defenses or tradeable resources, there was no great gain in doing much with Merseyside, so the Romans seemed to leave it as it was.
As some defenses against Irish raiders were placed on the Wirral (Meols) it wouldn’t have been surprising if a garrison had been placed somewhere like Formby, but there hasn’t been any evidence found, and it may be that with the lack of roads ( or things worth protecting), the Romans had better things to do with their time than worry about an obscure beach or fishing settlement having the occasional raid.