SkyTeam: Humanitarian & Missionary Fares: Proof of Eligibility
The Skyteam Missionary fares are exclusively meant for Missionaries and therefore there is a possibility the airline will ask for proof of your eligibility for these tickets.
Make sure you have proof with you when you travel.
The Fare rules reads as follows:

If you are traveling on a special humanitarian or missionary fare with SkyTeam airlines (including KLM, Air France, and Delta), please be aware that you and any accompanying family members must be prepared to provide proof of your eligibility at any point during your journey, including at check-in or during ticket audit.
This typically requires official identification or an original letter of mission/membership certificate on the letterhead of your non-profit humanitarian or bona fide missionary organization. For accompanying spouses and children, additional documentation proving family ties (such as a family registration book) may be required.
Failure to present valid proof of eligibility upon request will result in a fare adjustment. We strongly advise reviewing the full, extensive eligibility rules and required documentation provided by the airline to ensure compliance.