# Cells Sync: connection closed before server preface received

**URL:** <https://forum.pydio.com/t/cells-sync-connection-closed-before-server-preface-received/5838>\
**Category:** Sync Client\
**Tags:** solved\
**Created:** [April 4, 2024, 7:16pm UTC](https://forum.pydio.com/t/cells-sync-connection-closed-before-server-preface-received/5838 "2024-04-04T19:16:43Z")\
**Posts on this page:** 1\
**Showing post:** 9

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**Author:** ![c12simple](https://yyz2.discourse-cdn.com/flex032/user_avatar/forum.pydio.com/c12simple/32/90_2.png) [@c12simple](https://forum.pydio.com/u/c12simple)\
**Post date:** [April 5, 2024, 2:03pm UTC](https://forum.pydio.com/t/cells-sync-connection-closed-before-server-preface-received/5838/9 "2024-04-05T14:03:56Z")

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> [@taki-eddine](#):
>
> Is there any way to bypass GRPC, like I said before, Web and Android are working fine, I don’t understand the need for it for cells-sync 😅

Web & Android are base on restAPI, no local store

Cells-sync do the synchronization between cells & local store so **grpc** is used for synchronization.

> [@taki-eddine](#):
>
> ` **img4** `
> 
> ` **img5** `

Cells-sync has no interface to bypass the certificate (like you have in browser). You need to install the self-sign cert rootCA.pem to system trust root. Once the rootCA.pem is added to the system trust, your cells-sync can ‘trust’ this self-signed cert

> **[Installing the trusted root certificate](https://learn.microsoft.com/en-us/skype-sdk/sdn/articles/installing-the-trusted-root-certificate)**
>
> Installing a trusted root certificate is necessary only if you are notified that the certificate of authority is not trusted on any machine.

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