Upstream sent too big header while reading response header from upstream, client

I have been getting lots of error like this:

2020/03/30 00:43:08 [error] 14208#14208: *336392707 upstream sent too big header while reading response header from upstream, client: 172.68.189.93, server: noteplus.com, request: "GET /*%20cyrillic-ext%20*/@font-face%20%7B%20%20font-family:%20'Roboto';%20%20font-style:%20normal;%20%20font-weight:%20300;%20%20src:%20local('Roboto%20Light'),%20local('Roboto-Light'),%20url(https://fonts.gstatic.com/s/roboto/v20/KFOlCnqEu92Fr1MmSU5fCRc4EsA.woff2)%20format('woff2');%20%20unicode-range:%20U+0460-052F,%20U+1C80-1C88,%20U+20B4,%20U+2DE0-2DFF,%20U+A640-A69F,%20U+FE2E-FE2F;%7D/*%20cyrillic%20*/@font-face%20%7B%20%20font-family:%20'Roboto';%20%20font-style:%20normal;%20%20font-weight:%20300;%20%20src:%20local('Roboto%20Light'),%20local('Roboto-Light'),%20url(https://fonts.gstatic.com/s/roboto/v20/KFOlCnqEu92Fr1MmSU5fABc4EsA.woff2)%20format('woff2');%20%20unicode-range:%20U+0400-045F,%20U+0490-0491,%20U+04B0-04B1,%20U+2116;%7D/*%20greek-ext%20*/@font-face%20%7B%20%20font-family:%20'Roboto';%20%20font-style:%20normal;%20%20font-weight:%20300;%20%20src:%20local('Roboto%20Light'),%20local('Roboto-Light'),%20url(https://fonts.gstatic.com/s/roboto/v20/KFOlCnqEu92Fr1MmSU5fCBc4EsA.woff2)%20format('woff2');%20%20unicode-range:%20U+1F00-1FFF;%7D/*%20greek%20*/@font-face%20%7B%20%20font-family:%20'Roboto';%20%20font-style:%20normal;%20%20font-weight:%20300;%20%20src:%20local('Roboto%20Light'),%20local('Roboto-Light'),%20url(https://fonts.gstatic.com/s/roboto/v20/KFOlCnqEu92Fr1MmSU5fBxc4EsA.woff2)%20format('woff2');%20%20unicode-range:%20U+0370-03FF;%7D/*%20vietnamese%20*/@font-face%20%7B%20%20font-family:%20'Roboto';%20%20font-style:%20normal;%20%20font-weight:%20300;%20%20src:%20local('Roboto%20Light'),%20local('Roboto-Light'),%20url(https://fonts.gstatic.com/s/roboto/v20/KFOlCnqEu92Fr1MmSU5fCxc4EsA.woff2)%20format('woff2');%20%20unicode-range:%20U+0102-0103,%20U+0110-0111,%20U+0128-0129,%20U+0168-0169,%20U+01A0-01A1,%20U+01AF-01B0,%20U+1EA0-1EF9,%20U+20AB;%7D/*%20latin-ext%20*/@font-face%20%7B%20%20font-family:%20'Roboto';%20%20

and error like this too,

2020/03/30 04:24:24 [error] 14208#14208: *337435264 upstream sent too big header while reading response header from upstream, client: 172.68.142.79, server: noteplus.com, request: "GET /money-transaction/chapter-7/data:video/mp4;base64,%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

I have dig around and the possible solution is,

fastcgi_buffers 16 16k; 
fastcgi_buffer_size 32k;

Or adjust the size accordingly. But what I want to know is, what is causing such error and how to reduce the size of the header?

Any help is grateful.

Thank you