Digitonomy Ltd sent over five million unsolicited messages encouraging people to apply for cash loans via affiliates.
Investigating 1,464 complaints about the texts made between April 2015 and February 2016, the Information Commissioner's Office (ICO) found the company could not prove it had consent.
A company spokesman apologised to those people who found the texts "unwelcome".
The ICO's investigation revealed the company had used affiliates to send the messages and claimed they had proof of consent.
The ICO's head of enforcement Steve Eckersley said the wording of the consent examples were not sufficient and businesses that rely on direct marketing "must be able to confirm that people have given their permission to receive text messages".
"Depending on the word of another company is simply not acceptable and is not an excuse," he said.
A spokesman for Digitonomy said the company was "sorry that a reported 0.03% of recipients found the marketing messages from our appointed affiliate management company last year unwelcome".
He added that the company remained "determined to operate at all times within both the spirit and the letter of the law and best practice".
A Chester credit broker has been fined £120,000 for sending millions of text messages without permission.