Hello,
I believe there is a limitation somewhere (undocumented though) for contact imports. The HTTP response is a 500 because the request entity too large in the payload upon import.
For context: I have a VCF file with around 1,700 contacts that I was trying to import for testing purposes, and it errored out with Failed to import contacts (500). The VCF file I was using to import was 14.2 MB in size.
I could not find this documented, but the stack trace generated in the logs was pretty clear this was a size issue overall. Logs below.

Sep 03 22:31:11 ==> Starting contacts
Sep 03 22:31:12 CardDAV discovery: http://0.0.0.0:3000/.well-known/carddav
Sep 03 22:31:12 CardDAV server running at http://0.0.0.0:3000
Sep 03 22:31:12 Users authenticate with their email and app-specific passwords
Sep 03 22:32:59 at file:///app/code/node_modules/@cloudron/tegel/index.js:262:14
Sep 03 22:32:59 at Layer.handleRequest (/app/code/node_modules/router/lib/layer.js:152:17)
Sep 03 22:32:59 at Layer.handleRequest (/app/code/node_modules/router/lib/layer.js:152:17)
Sep 03 22:32:59 at Route.dispatch (/app/code/node_modules/router/lib/route.js:117:3) {
Sep 03 22:32:59 at getRawBody (/app/code/node_modules/@cloudron/tegel/node_modules/raw-body/index.js:116:12)
Sep 03 22:32:59 at next (/app/code/node_modules/router/lib/route.js:157:13)
Sep 03 22:32:59 at next (/app/code/node_modules/router/lib/route.js:157:13)
Sep 03 22:32:59 at read (/app/code/node_modules/@cloudron/tegel/node_modules/body-parser/lib/read.js:113:3)
Sep 03 22:32:59 at readStream (/app/code/node_modules/@cloudron/tegel/node_modules/raw-body/index.js:163:17)
Sep 03 22:32:59 at textParser (/app/code/node_modules/@cloudron/tegel/node_modules/body-parser/lib/types/text.js:34:5)
Sep 03 22:32:59 error: PayloadTooLargeError: request entity too large
Sep 03 22:32:59 expected: 14165817,
Sep 03 22:32:59 length: 14165817,
Sep 03 22:32:59 limit: 10485760,
Sep 03 22:32:59 path: '/api/addressbooks/5fa3c363/import',
Sep 03 22:32:59 status: 500,
Sep 03 22:32:59 type: 'entity.too.large'
Sep 03 22:32:59 {
Sep 03 22:32:59 }
Sep 03 22:32:59 }
Sep 03 22:34:29 at file:///app/code/node_modules/@cloudron/tegel/index.js:262:14
Sep 03 22:34:29 at Layer.handleRequest (/app/code/node_modules/router/lib/layer.js:152:17)
Sep 03 22:34:29 at Layer.handleRequest (/app/code/node_modules/router/lib/layer.js:152:17)
Sep 03 22:34:29 at Route.dispatch (/app/code/node_modules/router/lib/route.js:117:3) {
Sep 03 22:34:29 at getRawBody (/app/code/node_modules/@cloudron/tegel/node_modules/raw-body/index.js:116:12)
Sep 03 22:34:29 at next (/app/code/node_modules/router/lib/route.js:157:13)
Sep 03 22:34:29 at next (/app/code/node_modules/router/lib/route.js:157:13)
Sep 03 22:34:29 at read (/app/code/node_modules/@cloudron/tegel/node_modules/body-parser/lib/read.js:113:3)
Sep 03 22:34:29 at readStream (/app/code/node_modules/@cloudron/tegel/node_modules/raw-body/index.js:163:17)
Sep 03 22:34:29 at textParser (/app/code/node_modules/@cloudron/tegel/node_modules/body-parser/lib/types/text.js:34:5)
Sep 03 22:34:29 error: PayloadTooLargeError: request entity too large
Sep 03 22:34:29 expected: 14165817,
Sep 03 22:34:29 length: 14165817,
Sep 03 22:34:29 limit: 10485760,
Sep 03 22:34:29 path: '/api/addressbooks/5fa3c363/import',
Sep 03 22:34:29 status: 500,
Sep 03 22:34:29 type: 'entity.too.large'
Sep 03 22:34:29 {
Sep 03 22:34:29 }
Sep 03 22:34:29 }





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