I looked up this phrase in FGB, and got i gcleithiúnas a bheith. I also found in the dictionary in ainm a bheith ag obair, 'supposed to be working'.

I wondered if anybody else could confirm these and/or provide other translations that might work.

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I'm an intermediate speaker of the Corca Dhuibhne dialect of Irish and also have knowledge on the old spelling
Soir gaċ síar, fé ḋeireaḋ thíar

I never heard cleithiúnas in that sense
but:
bheith amuigh ar ...
bheith ceaptha (do ...) ...
ceapadh ...
bheith in ainm ...
+
... a bheith ... / ... go raibh ...

Thank you. So if I wanted to say 'It's not supposed to be easy', I could say níl sé amuigh air bheith furasta (or éasca), níl sé ceaptha bheith furasta/níl ceaptha dó bheith furasta, ní ceapadh bheith furasta, níl sé in ainm bheith furasta?

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I'm an intermediate speaker of the Corca Dhuibhne dialect of Irish and also have knowledge on the old spelling
Soir gaċ síar, fé ḋeireaḋ thíar

ní measfí go mbeadh sé éasca?

ní rud é go bhfuil ainm na héascaíochta air

Go raibh maith agat

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I'm an intermediate speaker of the Corca Dhuibhne dialect of Irish and also have knowledge on the old spelling
Soir gaċ síar, fé ḋeireaḋ thíar