An oral agreement is as enforceable as a written agreement -- it is just harder to prove. I suggest that you write a letter by certified mail, return receipt requested, to set out the terms of the oral agreement, the facts involved, your compliance with the agreement, and the other person's non-compliance, and to request that the other person honor the agreement. Partial performance of an agreement is typically evidence that the agreement exists (why else would the person undertake the time and expense of performance?), and can make the agreement enforceable.
If need be, you can use your letter as evidence in small claims court to prove up the agreement.
Save the text messages. They are also evidence of the terms of the oral agreement. Many people choose to handled smaller disputes in Small Claims Court, but it may be worth your while to hire an attorney to send a demand letter to the other party, to try to collect what they owe you without the need for litigation. Good luck.
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