There are 3 retention percentages:
It applies to most service providers and sales of goods. The base of incidence is 100%, that is, it is levied on 100% of the agreed price.
You must choose "the option" About: 100% - art. 101, paragraphs 1 and 9, of the CIRS"
There are, however, special situations in which the retention rate does not affect the entire price.
Applies to:
Physicians of clinical pathology, radiologists and pharmacists clinical analysts with a degree of disability equal to or greater than 60% can use this third option.
Therefore, since you are not exempt, you are more likely to have to withhold over 100% of earnings. The retention is made by the paying entity. The value of your receipt will be net of withholding and then at your IRS you will have to report the total of the withholdings you have made.