What is this error?

ERROR: for legionexchange-nginx Cannot start service legionexchange-nginx: driver failed programming external connectivity on endpoint local_legionexchange-nginx_1 (c6e1b698c28e270efd37ea3ad5cdf4593ba8b6411874f2c78b6d3a5a04cfa663): Error starting userland proxy: listen tcp4 0.0.0.0:80: bind: address already in use
ERROR: Encountered errors while bringing up the project.
Failed to start exchange! Please review your settings and try again.
[21:43] [server1.legion.exchange hollaex-kit] #

and

ERROR: for legionexchange-nginx Cannot start service legionexchange-nginx: driver failed programming external connectivity on endpoint local_legionexchange-nginx_1 (f182c431e34aada0bb6e4fd6fe0e455262d711932dd9513b43fdb5f20f96d8b2): Error starting userland proxy: listen tcp4 0.0.0.0:80: bind: address already in use
ERROR: Encountered errors while bringing up the project.
Failed to start exchange! Please review your settings and try again.