Can't build: "soap/soapH.h" is unavailable

[Groctel]

Hi!

I'm trying to build SWAD and am getting this output when running make:

make
gcc -Wall -Wextra -mtune=native -O2 -s   -c -o swad_account.o swad_account.c
gcc -Wall -Wextra -mtune=native -O2 -s   -c -o swad_action.o swad_action.c
gcc -Wall -Wextra -mtune=native -O2 -s   -c -o swad_agenda.o swad_agenda.c
gcc -Wall -Wextra -mtune=native -O2 -s   -c -o swad_alert.o swad_alert.c
gcc -Wall -Wextra -mtune=native -O2 -s   -c -o swad_announcement.o swad_announcement.c
gcc -Wall -Wextra -mtune=native -O2 -s   -c -o swad_API.o swad_API.c
swad_API.c:101:10: fatal error: soap/soapH.h: No such file or directory
  101 | #include "soap/soapH.h"  // gSOAP header
      |          ^~~~~~~~~~~~~~
compilation terminated.
make: *** [<builtin>: swad_API.o] Error 1

There are no other files named *soap* in the project:

swad-core on  master [?] 
➜ find . -name "*soap*"
./soap

Am I doing something wrong or is this a missing header file that needs to be added? Thank you!