Learn Italian: Non negozio il compenso, purché voi paghiate subito. - I do not negotiate the compensation, provided that you all pay immediately.

It does! However, in this sentence, negozio is the first-person singular ("I") form of the verb negoziare (to negotiate). You can tell it's a verb here because it directly follows the negative particle non and takes a direct object (il compenso).

Why is the verb pagare conjugated as paghiate instead of the regular present tense pagate?

Because of the conjunction purché (provided that / as long as). In Italian, conjunctions that introduce a condition or purpose require the verb that follows them to be in the subjunctive mood. Paghiate is the present subjunctive form for voi.

Why is there an "h" in paghiate?

To keep the hard "g" sound. The root of pagare has a hard "g" (like in "go"). When conjugating it into forms that start with "i" or "e", an "h" is added so the pronunciation doesn't soften into a "j" sound (like in "gel"). This spelling rule applies to the subjunctive forms of all verbs ending in -care and -gare.

Is the pronoun voi required after purché?