A support letter naming the entity, the profession, the duties and the engagement terms, plus written confirmation of the licence requirement and of where the work is performed.
Ask for documents, not reassurance
The most useful thing an employer can provide is specific and boring: a letter that names the employing entity precisely, describes the professional duties in operational language, identifies the listed profession being claimed, and states the period and terms of engagement. Ask also for written confirmation of the licence the role requires and of every location where the work will be performed, including any facility the employer does not itself operate. What the employer cannot supply is proof of the applicant's own credential or citizenship, which comes from the awarding body, the licensing board and a citizenship document.
Requesting these as documents rather than as assurances tends to surface disagreements early, which is exactly when they are cheapest to fix. Hypothetical example: a conservation-science analyst is hired to assess museum materials for a U.S. institution that uses a staffing affiliate.
A first review should separate applicant records from employer records: passport evidence and academic proof on one side; the duties letter, worksite list, payroll entity, and supervisor on the other. The executed offer and the affiliate’s authority to employ settle the latter point. Ask the institution to identify every site before the letter is final, then compare its duties language against the claimed profession.
Problems often arise when a generic human-resources letter says nothing about the actual work or names an entity that will not pay the worker. Correcting those facts before presenting the request is far easier than explaining inconsistent records later.