Short answer: do not use MDMA on your own for PTSD. MDMA is a controlled substance in most countries and, outside approved clinical trials, it is not an authorized PTSD treatment.
There is ongoing research into MDMA-assisted therapy, but it takes place only in regulated settings with trained professionals. Self-medicating or working with underground providers carries legal and safety risks.
Laws change and vary by country. I cannot verify your current local rules, but in many places MDMA and MDMA analogues are illegal for therapeutic use. Consider discussing legal options with a licensed clinician.
If you want background on MDMA analogues and how they are discussed in relation to therapy, see this overview: MDMA analogues and therapy.
Stay safe.