Te brindamos por la primer victoria

[poli]

Is this an error? I would certainly use primera victoria.

[Rusty]

This is an apocope, at best; it's considered an error or antiquated usage, otherwise. See here (https://www.rae.es/dpd/primero), especially point 1 c).
This usage would probably not be heard among the educated, but the press lets it slip by to correctly quote the individual who used it.

If we use uneducated speech (even when we don't realize it's uneducated), it can get printed, videoed, or repeated unedited.
I think that is what happened here. The press didn't change what was actually said or printed.

I find misspellings a lot. Some may be direct quotes, but the majority come from people that don't check to see if they've made mistakes before they hit the Enter key. For example, I just encountered a video with post-edited commentary. Not only did they use 'primer' incorrectly, they wrote 'portrero' (instead of 'portero'), 'equiipo' (instead of 'equipo'), and totally messed up the punctuation in a single, fragmented "sentence." Ugh!

[aleCcowaN]

"primer victoria" is abdolutely, definitively correct in many a country, despite the efforts of some to "limpiar, fijar y dar esplendor".

"El uso de la forma apocopada ante sustantivos femeninos (la primer vez), normal en el español clásico y que pervive en alternancia con la forma no apocopada en el español americano, se considera hoy un arcaísmo que es preferible evitar en el habla culta"

Source RAE's (co-opted and changed) DPD

Translation: "the evil polititians say in a nonchalant and feigned way that if you are using it you are a brute". They typically resort to such métodos obscuros que _e_lucubran magistralmente.

The use typically is

su primer vez
la primera vez

¡Brindamos por tu primer victoria! (We raise our glasses to your first victory)
Te brindamos tu primer victoria (We gave/give you your first win/victory)
Te brindamos la primer/a victoria (We gave/give you our -whether you are included or not- first win/ victory)

With "brindar" meaning to give as an offering or gift, to make it possible or to concede