film – 155a Speedlite Flash not firing from hotshoe on Canon AE-1

Like the title says the hot shoe won’t fire the flash from some reason. I have the shutter speed set to 60 and the f stop on auto as I should. The test button on the 155a fires and shorting two of the hot shoe connectors fires the flash but the shutter button won’t for whatever reason. I can see that the camera picks up the the flash unit because the light meter is locked on the appropriate f stop but I have no luck getting it to fire the flash. Using the sync port on a different, non-hot shoe flash unit works but I have no way of testing sync port on the 155a. I’ve also tried cleaning the hot shoe connections.

Any help would be appreciated.