springboot application.properties

verify if you have this items:
@Bean
public CommonsMultipartResolver multipartResolver() {
CommonsMultipartResolver multipart = new CommonsMultipartResolver();
multipart.setMaxUploadSize(3 * 1024 * 1024);
return multipart;}

@Bean
@Order(0)
public MultipartFilter multipartFilter() {
MultipartFilter multipartFilter = new MultipartFilter();
multipartFilter.setMultipartResolverBeanName("multipartResolver");
return multipartFilter;
}

and in the pplications.properties

# MULTIPART (MultipartProperties)
spring.http.multipart.enabled=true
# Enable support of multi-part uploads.
# spring.http.multipart.file-size-threshold=3 # Threshold after which files will be written to disk. Values can use the suffixed "MB" or "KB" to indicate a Megabyte or Kilobyte size.
spring.http.multipart.location= /
# Intermediate location of uploaded files.
spring.http.multipart.max-file-size=10MB
# Max file size. Values can use the suffixed "MB" or "KB" to indicate a Megabyte or Kilobyte size.
spring.http.multipart.max-request-size=10MB
# Max request size. Values can use the suffixed "MB" or "KB" to indicate a Megabyte or Kilobyte size.
spring.http.multipart.resolve-lazily=false
# Whether to resolve the multipart request lazily at the time of file or parameter access.