Q: We discovered a copyright agreement breach after publishing our research paper. What action should we take?

I used an evaluation measure created overseas for a clinical study to investigate the effect of a medical treatment. Upon use of this evaluation measure, an agreement for usage was required, so I directly communicated with the creator of the measure, and paid some money and signed an agreement. After my study for investigating the effect was published, the creator of the measure told me that my usage of the measure was in breach of the agreement. When I checked the agreement, surely, I did some violation against the agreement. Specifically, 1) the 1-year agreement was exceeded by 2 months , 2) wording about copyright protection for the measure was not described in Result section and Acknowledgements, 3) designated references were not completely cited. To solve this violation, 2 options were shown from the creator side. One is that we invite the creators from overseas and arrange the lecture about how to use the measure for all the institutions involved in our study (+ 1.3 million yen). The other is that we ask the journal where our paper was published to revise the paper (+ 1.7 million yen).

In this situation, what action should we take?