Joining two Dynamics 365 entities using LookUp()

[Anonymous]

Hello,

For testing, i created an App that is mean to display on the same screen the name of all my active accounts, and its primary contact name, connected both Contacts and Accounts entities from my Dynamics 365 environment.

I have already filtered the displaying accounts list, but when triing to show its primary contact using the following code 

LookUp(Contactos;_parentaccountid_value=ThisItem.accountid; name)

I get an error telling me that this is an invalid expression, no further details.

Tried several other ways of joining them, but i always get this or a binary exception telling me that i can't compare edm.guid and edm.string.

Not sure if i am missing any key concept, or i do have to group table before, or what is the issue

Thanks you in advance.