What is the legal ruling on taking free drinks from a coffee company due to an error in their application, and is that considered theft or unlawful (haram)?

Not every unlawful appropriation of money is considered theft that mandates a prescribed punishment (hadd), as there are differences between theft, betrayal (khiana), looting, and usurpation. What the questioner mentioned is not considered theft that mandates a prescribed punishment, due to the absence of the conditions for its imposition, such as the safeguarding of the property (hirz) and stealth.

A Muslim is generally forbidden from unlawfully appropriating money and from betrayal altogether. The property of another is unlawful and is not permissible except with their willing consent.

The existence of flaws in the implementation of the company does not permit the unlawful appropriation of its money. The conditions of the company must be adhered to. Therefore, the questioner must pay the company the price of what he took without right, or seek their forgiveness and pardon, or settle with them regarding their right.