If MFLink never gets past “Synchronization in progress” or “Boarding” when you fly in X-Plane, the most likely cause is your XPUIPC version.

Why it happens #

XPUIPC now exists as two separate products. The classic XPUIPC (version 2.0.x) works with MFLink. The newer XPUIPC+ restarts its numbering at 0.x and is a different plugin: MFLink does not currently work with it. Because its version number looks lower, it is easy to install it by mistake.

Step 1: Check which plugin you have #

1. Open your X-Plane folder, then Resources > plugins.
2. If you see a folder named XPUIPC+, you have the new version.

Step 2: Remove XPUIPC+ #

1. Close X-Plane and MFLink.
2. Delete the XPUIPC+ folder from Resources > plugins.

Step 3: Install XPUIPC 2.0.3.5 #

1. Download XPUIPC 2.0.3.5 + XPWideClient 2.0.0.3 from the XPUIPC repository (third-party site). Take that exact entry, not the newer builds listed above it, then extract the archive.
2. Copy the XPUIPC folder directly into Resources > plugins. Make sure it is not nested inside another XPUIPC folder.

Step 4: Check and fly #

1. Start X-Plane and load your aircraft.
2. Open the Plugins menu: XPUIPC must be listed.
3. Start MFLink and launch your flight.

If MFLink is still stuck, follow How can I fix synchronization issues between MFLink and FSUIPC/XPUIPC?, then open a support ticket.